The invention relates to a ball for use, e.g., in football training, physical therapy, and early childhood physical education.
The use of large, heavy balls, known as "medicine balls" for weight training, has long been known. Medicine balls have traditionally consisted of a stiched leather cover filled with heavy wool shearings, KAPOK filler or the like. These balls have a tendency to deform or lose their shape because of the softness and pliability of their stuffing. Further, it is difficult to make a large diameter ball (greater than 18") using this construction because the weight of the filler would make it excessively heavy. Outdoor use of medicine balls is typically impracticable because the elements have a deleterious effect on the ball, e.g., the filler is susceptible to rotting and the surface is slippery when wet.
In 1970, General Plastics Manufacturing Co. introduced a large, heavy ball for use as a football training tool, sold under the trademark LAST-A-FOAM.RTM. ball. This ball was 30" in diameter with an inner core of plastic and an outer covering of vinyl. The ball was assembled by adhering two halves together to form a ball.
While the LAST-A-FOAM.RTM. ball overcame some of the problems associated with making a large diameter ball having a reasonable weight, the ball had other defects, such as a tendency to develop surface cracks, split in half along the glue seam where the two halves were adhered together, and become slippery when wet.